Researchers at MIT—Prof. Daniel Nocera and Dr. Matthew Kanan—have developed a new water-splitting catalyst that is easily prepared from earth-abundant materials (cobalt and phosphorous) and operates in benign conditions: pH neutral water at room temperature and 1 atm pressure. A report on their discovery was published online 31 July 2008 in the journal Science.

The cobalt-phosphorous catalyst targets the generation of oxygen gas from water—the more complex of the two water-splitting half-cell reactions required (H2O/O2 and H2O/H2). Another catalyst generates the hydrogen. Although the new catalyst requires further work, it opens a very promising pathway for the development of systems that use artificial photosynthesis to store solar energy on a large scale in the form of O2 and H2 for subsequent use in a fuel cell.

Of the two reactions, the H2O/O2 reaction is considerably more complex. This reaction requires a four-electron oxidation of two water molecules coupled to the removal of four protons to form a relatively weak oxygen-oxygen bond. In addition to controlling this proton-coupled electron transfer (PCET), a catalyst must tolerate prolonged exposure to oxidizing conditions. Even at the thermodynamic limit, water oxidation requires an oxidizing power that causes most chemical functional groups to degrade. Accordingly, the
generation of oxygen from water presents a significant challenge toward realizing artificial photosynthesis.

—Nocera and Kanan (2008)

Other water oxidation catalysts exist, including first-row spinel and perovskite metal oxides; and precious metals and precious metal oxides. The first requires concentrated basic solutions (pH>13) and moderate overpotentials (<400 mV); the second operate under acidic conditions (pH<1).

However, few catalysts operate under the conditions of photosynthesis, i.e. in neutral water under ambient conditions. Neutral water is oxidized at Pt electrodes and some precious metal oxides have been reported to operate electrocatalytically in neutral or weakly
acidic solutions. The development of an earth-abundant, first-row catalyst that operates at pH 7 at low overpotential remains a fundamental chemical challenge. Here we report an oxygen-evolving catalyst that forms in situ upon anodic polarization of an inert electrode in neutral aqueous
phosphate solutions containing Co2+. Oxygen generation occurs under benign conditions: pH = 7, 1 atm and room temperature.

—Nocera and Kanan (2008)

The new catalyst consists of cobalt metal, phosphate and an electrode, placed in water. When electricity—whether from a photovoltaic cell, a wind turbine or any other source—runs through the electrode, the cobalt and phosphate form a thin film on the electrode, and oxygen gas is produced. Combined with another catalyst, such as platinum, that can produce hydrogen gas from water, the system can duplicate the water splitting reaction that occurs during photosynthesis.

James Barber, a leading researcher in the study of photosynthesis who was not involved in this research, called the discovery by Nocera and Kanan a “giant leap” toward generating clean, carbon-free energy on a massive scale.

This is a major discovery with enormous implications for the future prosperity of humankind. The importance of their discovery cannot be overstated since it opens up the door for developing new technologies for energy production thus reducing our dependence for fossil fuels and addressing the global climate change problem

—James Barber, the Ernst Chain Professor of Biochemistry at Imperial College London

Currently available electrolyzers, which split water with electricity and are often used industrially, are not suited for artificial photosynthesis because they are very expensive and require a highly basic (non-benign) environment that has little to do with the conditions under which photosynthesis operates.

If artificial photosynthesis is to enable the storage of solar energy
commensurate with global demand, water-splitting chemistry will need to be performed at a daunting scale. Storing the equivalent of the current energy demand would require splitting greater than 1015 mol/yr of water, which is roughly 100 times the scale of nitrogen fixation by the Haber Bosch process. [The Haber Bosch process allows the mass synthesis of ammonia from nitrogen and hydrogen.]

The conditions under which water splitting is performed will determine how solar energy is deployed. The catalyst reported here has many elements of natural photosynthesis including its formation from earth abundant metal ions in aqueous solution, a plausible pathway for self-repair, a carrier for protons in neutral water and the generation of O2 at low overpotential, neutral pH, 1 atm and room temperature.

—Nocera and Kanan (2008)

More engineering work needs to be done to integrate the new scientific discovery into existing photovoltaic systems, but Nocera said he is confident that such systems will become a reality. Nocera is the principal investigator for the Solar Revolution Project funded by the Chesonis Family Foundation and co-Director of the Eni-MIT Solar Frontiers Center.

This is just the beginning. The scientific community is really going to run with this.

—Daniel Nocera

Nocera hopes that within 10 years, homeowners will be able to power their homes in daylight through photovoltaic cells, while using excess solar energy to produce hydrogen and oxygen to power their own household fuel cell. Electricity-by-wire from a central source could be a thing of the past.

The project is part of the MIT Energy Initiative, a program designed to help transform the global energy system to meet the needs of the future and to help build a bridge to that future by improving today’s energy systems.

This project was funded by the National Science Foundation and by the Chesonis Family Foundation, which gave MIT $10 million this spring to launch the Solar Revolution Project, with a goal to make the large scale deployment of solar energy within 10 years.

I don't know what the efficiency of this process is, but let's just assume 50% for aguments sake. Let's be generous and say you can convert the hydrogen 'fuel' into electricity in a very efficiency FC at 65% efficiency. This is still only a 33% recovery of the original electricity that was converted. Almost every other form of energy storage will be more desireable.

Cobalt based catalysts have been used for decades in the electrolysis of water. Their oxygen evolution activity is thousand times higher in alkaline solution than what Kanan and Nocera report for neutral water (1 mA/cm2 at an overvoltage of 0.41 V). Still, the efficiency of splitting water into hydrogen and oxygen by electrolysis is only around 70%. The efficiency of storing hydrogen at high pressure is about 90% (only 70% if hydrogen is liquefied). Fuels cells, which convert hydrogen back into electricity, are about 40% efficient under practical conditions. Hence, the overall efficiency of storing (solar) electricity as hydrogen is 0.7 * 0.9 * 0.4 = 25%. By comparison, lithium batteries are more than 80% efficient in storing electricity.

Kanan and Nocera propose to store solar energy directly by splitting water with an artificial photosynthetic system (photoelectrochemical cell) instead of having separate solar cells for electricity generation and water electrolysers for hydrogen production. The idea is certainly attractive, but it faces serious difficulties in practice.

First of all the current densities and hence gas evolution rates of photoelectrodes in sunlight are hundred times lower than in an electrolyser. The highly diffusive and volatile hydrogen has to be separated from oxygen (by a membrane that conducts protons) and collected over the whole surface of the solar array. The water consumed by splitting has to be replenished and mixed with electrolyte salts for electrical conductivity.

Water splitting requires theoretically a voltage of 1.23 V at 25 C, practically about 1.8 V due to overvoltage losses. To produce this voltage with visible light at least two photosystems have to be connected in series, as plants have been doing for billion years with photosystems I and II.

To summarize: you need at least two illuminated electrodes connected to catalysts for hydrogen and oxygen evolution, separated by a membrane, bathing in an aqueous electrolyte that is continuously renewed and a system to collect the hydrogen without mixing it with oxygen. The distance between the electrodes has to be kept very short (a few millimetres) in order to limit ohmic resistance losses in the electrolyte. And the whole has to be stable under sunlight and heat for many years…

Isn’t it much easier and more practical to connect a field of photovoltaic panels, which are optimized for solar energy conversion, to a compact electrolyser that is optimized for hydrogen generation? But, as mentioned above, electricity is by far more efficiently stored in batteries. And if you just want to store solar energy during the night the storage of heat in solar thermal power plants is the cheapest and most efficient solution.

Does the average private house solar panel installation provide an energy excess during the day?

This isn't relevant. The "average" installation is changing rapidly. We should be looking at the amount of energy available from a typical roof, and the answer is "yes, there should be a large excess".

Whether this excess should be converted to hydrogen or distributed via the grid is another question.

if you can produce hydrogen at sea level, and recombine it with oxygen at some height above sea level with the byproduct of water, could you use the lift of the hydrogen and the weight of the water to drive another wheel which also generates electricity?

Heat of combustion of hydrogen: 70600 cal/mol (higher heating value)
This is about 296 kJ/mol.

1 mole of hydrogen is 2 grams, which displaces 29 grams of air. If it rises 1 kilometer, the force of buoyancy would generate 265 joules of energy before losses. The hydrogen combines to make 1 mole of water, 18 grams. Falling by 1 kilometer yields 177 joules of energy before losses. The total theoretical energy available from a kilometer of rise is about 440 joules, or a bit more than 0.1% of the energy of combustion.

After reading some other articles, I THINK what was developed is a safer, less expensive form of electrolyzer. No base or acid solutions are needed, but more importantly, the entire system is low cost. There are no substantial efficiency improvements, as far as I can tell.

What does this mean? Well, potentially, something significant. If the electrolyzer technology is inexpensive, then its use or non-use become less problematic from an economics standpoint. This means that the system can remain idle due to intermittent input from renewable sources such as wind or solar.

It doesn't matter if there is no hydrogen fuel cell to receive the hydrogen, as cheap hydrogen can be easily combined with carbon (from abundant CO2) to produce methane, which has an extant infrastructure and consumption base.

So it doesn't get around the electricity cost, but it might get around the electrolyzer cost of hydrogen production. Too bad the researchers didn't indicate the expect cost of the system in dollars per kilowatt.

The source article is so poorly written that it is hard to get a real sense of the significance of this discovery. Does the MIT group envisage this new electrode a path to cheaps electrolyzers, or are they hoping to create a photo-electrolysis system that directly uses solar photons rather than elecric current to drive water splitting? Also the emphasis on a PV/electrolzer/Fuel cell combination for domestic electricity is unfortunate. If Reasonably cheap hydrogen from renewable resources becomes available then the most immediate tangible benefit will be to put a ceiling on the price of ammonia fertilizer. Since the cost of natural gas is currenty 90% or more of the cost of ammonia, renewable hydrogen has to be able to compete in this arena or it will be too expensive to be useful.

I have a question. Maybe it's because I'm from the desert and water is very precious to us. The Earth has the same amount of water on it today that it did a billion years ago. I know we have found 100s of ways to make water dirty even radioactive. However given time or filters it will clean up. This process DESTROYS water, not only that but it DESTROYS potable water and if hydrogen is the future then we will be DESTROYING potable water on a massive scale. Someone enlighten me, because this thought scares the crap out of me. I might be able to survive without oil or electricity but without water I'm dead.

So if this all takes place in one location, like a home, the transport and storage issues associated with hydrogen are greatly lessoned, but do not go away. Even in a personal home type system you will still need some type of storage and you will still have leaking, metal crystallization and very real safety issues.

Again, remain open to all ideas because we need all the energy we can get. The ability to get renewable energy from multiple sources simultaneously such as wind, PV and Solar thermal is one of the great advantages of a future powered by truly renewable energy.

If something works, we should jump on it. Nukes work. We know that. But Nukes cost so much and make such a costly mess that heading down the Nuke road would suck up resources better spent on truly renewable options using fuel that never pollutes, never goes up in price and is available as long as the sun shines.

Being open minded is not enough. We must constantly practice cold hearted triage as we pick our renewable energy battles.

If green electricity can be had for $0.06 per kiloWatt-hour, then about 55 kiloWatt-hours is needed to make a kilogram of H2. Or $3.30 per kg. Or about $26.40 per MMBTU. This compares with making H2 from NG ($15/MMBTU). Not so good.

If the electricity cost could drop to $0.03, then we'd be at about $13.00 per MMBTU, probably competitive.

Cost of electrolyzer just raises these prices more, so an incremental improvement in that area helps, but overall cost is dominated by electricity cost.

One to three times a week for the last 50 years I have been hearing "solar power will be ready in the next ten years".
If you are waiting on Uncle Sam or the oil companies to get it right we will all be in trouble that we can't solve in less than ten years. It is getting hotter and dryer every year and our water table is going down. Food for fuel is not very inteligent and it requires more water to be pumped for irrigation.
We have to solve this energy/food/water issue soon.
This planet will not keep us all alive without our help. If we continue doing what we have been doing we will continue getting less what we are getting.
We better start using more of the sun and it's effects (wind,solar, wave,....ect)NOW or the population will soon start to decline.
WRITE to and tell your congress person to stop nation building in a far away place and build this nation to be able to support our people first.

"The QuantumSphere Nano NiFe electrodes are intended to accelerate the clean production of hydrogen through electrolysis and reduce industrial dependence on production methods that result in the net production of greenhouse gases," said Kevin Maloney, president and CEO, QuantumSphere, Inc. "Now with the use of our Nano NiFe coating, we are literally splitting the water more efficiently and turning heads in the scientific, industrial, and transportation communities. QuantumSphere's long-term commitment to enabling the clean-energy economy takes another step forward through the introduction of these low-cost electrodes."

@Lee,
Still have doubts? Even when the world is now setting standards for the eventual Hydrogen economy?

@oldneil Is it a 1 to 1 conversion. My brain is going 'that's imposible'

@Just Watching I've been waiting 30 years for solar to get reasonable myself. The population is the problem, if you think that we are putting a strain on the environment with 6.7 billion wait till there is 8.7 billion. My 16 month old should be graduating high school about then.

Solar is cost effective, both PV and heat. It is the initial cash outlay that you dislike. In the 30 years you have waited, it would have paid for itself as compared to low energy costs! The fact remains, the most expensive solar products pay for themselves in well less than 1/2 your adult lifetime. Today, with high energy costs, the payback time is much shorter.

The above process, which improves energy collection effectivity looks to be a nice step forward.

This process DESTROYS water, not only that but it DESTROYS potable water and if hydrogen is the future then we will be DESTROYING potable water on a massive scale.

I'm going to let you in on a little secret here (don't tell anyone, because the world might panic if it got out):

GREEN PLANTS destroy potable water. The oxygen released during photosynthesis is obtained by the breakup of water molecules. Also, the earth's water isn't permanent; water is photolyzed to hydrogen and oxygen in the upper stratosphere, and hydrogen can escape permanently into space.

But we've made it 4-odd billion years so far, so we should be good for the next few hundred million (until the Sun's increasing output turns Earth into a copy of Venus).

@Engineer - GREEN PLANTS destroy potable water. The oxygen released during photosynthesis is obtained by the breakup of water molecules.

I do not believe this is correct. The oxygen released during photosynthesis is obtained by the breakup of co2 molecules. The plant photo splits off the carbon and the plant uses it as fuel the O2 is released as waist gas (lucky us). The water molecules are used to deliver nutrients from the soil and is the hydrant for the support system of the plant. The water molecules escape through the skin of the plant cleaned and unmolested.

Joseph,
Hydrogen will react with O2 in the upper atmosphere when triggered by UV light to form H2O, so it won't escape into space. As long as there is an abundance of O2 in the atmosphere, there will be little chance of H2 escaping into space.

Hydrogen from water elecrolysis is one sixth endothermic. The thermodynamic limit is 83 percent. If these researchers claim 83 percent, they have not been paying attention to the concept of entropy.

Let's give them the benefit of the doubt and say that they'll get the thermodynamic limit of 83%. Fuel cell efficiency at a net 50% HHV is very optimistic when all losses are considered. With miscellaneous losses that's perhaps 40% round trip efficiency.

You can see why hydrogen energy storage doesn't work.

Hydrogen is great for chemical feedstock, and perhaps in the future for liquid fuels production for niche applications. And great rocket fuel.